The present invention relates in general to protective armor, and, in particular, to ceramic-based integral armor.
Desired armor protection levels can usually be obtained if weight is not a consideration.
However, in many armor applications, there is a premium put on weight. Some areas of application where lightweight armor are important include ground combat and tactical vehicles, portable hardened shelters, helicopters, and various other aircraft used by the Army and the other Services. Another example of an armor application in need of reduced weight is personnel body armor worn by soldiers and law enforcement personnel.
There are two prevalent hard passive armor technologies in general use. The first and most traditional approach makes use of metals. The second approach uses ceramics. Each material has certain advantages and limitations. Broadly speaking, metals are more ductile and are generally superior at withstanding multiple hits. However, they typically have a large weight penalty and are not as efficient at stopping armor-piercing threats. Ceramics are extraordinarily hard, strong in compression, lighter weight, and brittle, making them efficient at eroding and shattering armor-piercing threats, but not as effective at withstanding multiple hits. Lighter-weight metallic and ceramic armor designs are known. For example, metals such as titanium and aluminum alloys can replace traditional steel to cut weight. Ceramics, such as aluminum oxide, silicon carbide, and boron carbide, are used in combination with a supporting backing plate to achieve even lighter armor.
State-of-the-art integral armor designs typically work by assembling arrays of ballistic grade ceramic tiles within an encasement of polymer composite plating. Such an armor system will erode and shatter projectiles, including armor-piercing projectiles, thus creating effective protection at reduced weight. Various designs are in current use over a range of applications. Substantial development efforts are ongoing with this type of armor, as it is known that its full capabilities are not being utilized. For example, there is a large body of information which shows that confining the ceramics results in an increase in penetration resistance.
In the laboratory, ceramics show much higher performance when their boundaries are heavily confined. The two key parameters are suppression of cracked tile expansion and putting the ceramic in an initial state of high compressive stress to delay or stop it from going into a state of tensile stress during impact. The problem is to devise methods to realize some or all of this confinement effect so it can be reduced to practical application in real armor systems. If the ceramic tile is not encased, the fractured pieces can move away easily, and residual protection is lost. Snedeker, et al. used a hybrid metal/ceramic approach in U.S. Pat. No. 5,686,689. Ceramic tiles were placed into individual cells of a metallic frame consisting of a backing plate and thin surrounding walls. A metallic cover was then welded over each cell, encasing the ceramic tiles.
Multiple hits are a serious problem with ceramic-based armors. Armor-grade ceramics are extremely hard, brittle materials, and after one impact of sufficient energy, the previously monolithic ceramic will fracture extensively, leaving many smaller pieces and a reduced ability to protect against subsequent hits in the same vicinity. Further, when the impact is at sufficient energy and velocity, collateral damage typically occurs to the neighboring ceramic tiles. Schade, et al. (U.S. Pat. No. 5,705,764) used a combination of polymers and polymer composites to encase the ceramic tiles in a soft surround to isolate the tiles from one another, reducing collateral damage.
An object of the present invention is to increase penetration resistance and decrease collateral damage of ceramic tile armor arrays, while maintaining or lowering the armor system weight.
Further objects, features and advantages of the invention will become apparent from the following detailed description taken in conjunction with the following drawing.